I've installed ubuntu server on a VirtualBox virtual machine and now I'm trying to follow a tutorial that says I need to install a package called csh. When I type this line

sudo apt-get install csh

I get "unable to locate package csh". This happens with all 4 other packages I tried to install. I'm not sure what I'm doing wrong. Perhaps the VM can't reach the Internet. How do I check, or troubleshoot this?